Filtering system



Aug. 13, 1929.

R. AUDUBERT FILTERING SYSTEM Filed Maren 7. 1928 3 Sheets-Sheet iii: 20

INVENTOR F016 z/a/fr/ BY C ATTORNEY Filed March 7, 1928 3 Sheets-Sheet 2 Aug. 13, 1929. R. AUDUBERT FILTERING SYSTEM Filed Maron 7, 192e;v

5 Sheets-Sheet 5 INVENTOR Fen( /z/dz/ber A'I TORNEYS PatentedA Aug. 13, 1929.

UNITED STATES Y Y 1,723,997' PATENT OFFICE.

AUDUBEBT, F PARIS, FRANCE. Y

FETERING SYSTEM.

`App1ication led Iarch 7, 1928, Serial No. 259,705, and in France October 27,1927.

The ordinary definition of a filter is a. de.

vice for strainingA impurities out of a liquid. This gives a very accurate picture of the operation of the ordinary filter Where the impuri- 5 ties are held back by mechanical interference. Due to the fact that the. usual filter holds the impurities mechanically, pressure on the liquid does not decrease the efficiency of action and greatly increases `the amount o'E liquid that can be put through a givenyiilter in a given time. ln most cases,vthe filtering` medium is so coarse in comparison to the size of the impurities that when the flow first starts, the finer impurities will pass through, and a clear flow will not be had until the passages of the filter have been somewhat clogged. Thus there is a steadyincrease in efiiciency as re' gards completeness of removal but this lis necessarily accompanied Vby 'a steady falling off in efficiency as` regards amount ,of liquid which passes through.

I have discovered that by utilizing the electric phenomena which occur in small tubes it is possible to construct a filter which will give a substantial commercialv flow, will give as complete removal ofimpurities from the first drop that passes through as fromthe later part of the iiow and will not become blocked inside the passages, so that if the impurities collect on the face of the filter and impede the flow of liquid to the filter, a surface scraping Will restore approximately the original con` ditions.

lt is known that there is usually a difference of potential between two heterogeneous phases. Whatever b e the theory of this phenomenon, it results in electric attraction and repulsion actions which can be utilized for the separation from a liquid of' material of diierent phase. I have found that to obtain eliicient filtering action from a tube of a diameter greater thanA that of the particles` to be removed, a balance must be maintainedbe-- tween the diameter of the tube, the ield of electric ctions at the inner surface and the static hea on the liquid to be ilteredfwhich there is asuicient Aelectric field. when the conditions stated are met, the electric-fields in the tubes will exercise a. selective action be tween the liquid and the matter held in suspension. As to such suspended matter, the

there is thus formed on the face of the filter Y,

a felted layer of the impurities which does not repel or materially interfere with flow of the liquid. At the same time, since this layerv h as the same sign as the dispersed `impurit1es 1t appears to repel them more and more asthe thickness of the layer increases, and Y thus the layer will'V tend to build up very gradually and eventually will reachA a point of substantial equilibrium. vOf course the compactness of this layer will be le'ss where gravity is Working against its formation',

Where the tube wall and the impurities .both have the same sign a. like action will start at once Without the necessity of having particles of the impurities collect around the entrance to the tube in order to cause repulsion to exist. In this case, there is also a further factor tending to assist in the desired separation. When a liquid passes slowlyinto a tube, the walls ot which carry an electrical charge -having -an effective ield over the cross sectional area of the tube, there isa measurable diiierence in potential between diferent prtions of the liquid in the tube, and the portion near the entrance to the tube will have a like sign to the tube Walls. A In other words, the ions with the opposite sign to the tube walls are drawn into the tube, and the ions with the same sign remaln near the entrance, thus creating a. polarized Vfield of increasingV intensity which will tend to repel impurities of like sign from the entrance to the tub'e. `1 This is particularly important when the tube Walls have the same sign as the impurities. for where this is the case, if an impurity vonce enters thetube, it will notv be removed by the attraction of the walls but may-'becarried through. Accordingly, whileI preferto vwhere the impurities have a natural tendency similar phenomenamay occur adjacent thev loose layer of impurities that will collect on the face of the filter, which will be a factor in reaching the equilibrium referred to.

Under some circumstances as for example to coalesce and form a more or less impervious layer, it maybe desirable to take steps to give to the wall of the tube a definite electric charge of like sign to that of the impurities, by utilizing factors recognized under the known laws of the electric forces of adsorption. A practical method of giving a desired charge is by impregnating'the ltering material.

lThus one may give to the surface of the filtering material a positive charge by the use ofany of the acids, particularly phosphoric acid.

In this case the hydrogen ions are employedto create a positive charge. In addition, poly- Ivalent cations such Vas cerium, or lanthanum or other similar materials may be used.

To provide anegative charge, all bases may be employed, in which case the hydroxyl' ions serve to create` the negative charge on they filter. Algo polyvalent anions such for ex-A y ple as ferro-cyanide (FeCsNe) may be use Thus far, the discussion has not taken into account the question of velocity of the liquid in the tube. It must be borne in mind that the electrostatic forces that have been referred to may be quite minute near the centre of the tube, particularly where the radius of the tube is approximately equal to the ef fective field of the electric action of its walls, and therefore unless thev velocity ofthe liquid is kept down to a minimum such action will be upset and` the impurities will be swept through, unless of course an ordinary mechanical strainingeffect is built up which may be effective for a short time, after which the filter clog. From this itfollows that the velocity must be low enoughftaking into account the length and diameter of the tubes and the electric charges, so that impurities will not be swept through without being acted upon by the charge. The evidences of correct conditions are ,that the liquid will be purified right from the start, -and after the filter has been in operation some time it will come to a -substantial equilibrium beyond which point its flow will not be materially reduced by the collection of the layer of impuritics against the face of the` filter. This f point will usually be reached after a relatively long operation and if one desires to clean the lter before the rate of flow drops to this peint of equilibrium it is simply necessary to scrape away the relatively loose material on the surface, for no substantial amount Will be found choking the pores on the inside. The best effect is obtained by having lthe force of gravity working against the flow of the liquid, as this 4will help to keep the impurities from entering, or settling on and packing against the tubes.

. From this discussion it will be noted that one of the outstanding features of my filter .is`that the liquid passages are suiciently large so that from a mechanical point of View impurities can pass through the openings', but because of the operations being conducted at low velocities, the electrical forces are permitted to act to prevent such passage. Thus'while a very low velocity is maintained through the ilter it must be remembered that the size of the passages remains relatively large and thus an efficient rate of flow can be maintained. If undue pressure is utilized 'with a lilter intended for'operation accord` ing to my method, then the device' will function in the old and Well-known Way, namely, impurities will come through until the passages are partially choked, t-hen there will be a relatively short period of eiicient action until the pores become blocked to the pointwhere the flow is reduced ,below the point of practical yield. v

In operation, I have found that etlicient results can be obtained as for example 'inD filtering transformer oil at a temperature of 50 C. by using fabric Woven like an ordinary lamp wick but only .about 5 centimeters long,

through which the liquid rises, and main-4 taining a pressure differential only barely suiiicient to cause a iiow to take place. Such I pressure dilerential may be in the order of a pressure equivalent to a static head of from 5 to 100 centimeters-of water, but it is understood that theseffigures are given rather by way of illustration than in limitation and that. it' velocity rather than the pressurefrijl tch is important so that the viscosity of-',tle" liquid must be considered; further the permissible velocity will vary with the size of the tubes and the force of their electrostatic charge.

-The simplest Way to maintain the desired pressure differential is to arrange the tubes in a casing which will permit the lower ends to contact with the oil but will prevent the entrance of air or liquid to the upper portion `so that the entrance can 'only take place through the tubes. `The filtered material is collected lfrom the upper portion of' such casing. When such a casing is provided, the pressure differential may readily be obtained in various Ways such as maintaining the top level of the liquid to be iiltered, above the top of the tubes, or by 'slightly reducing the plying outside suction to start the flow.

In view of the low pressure diii'erential used, it isi highly desirable thatthe tubes be of the same length, for inasmuch as the tubes must be quite small, internal friction will be acfactor of importanceand if the tubes arc of substantially different length a pressure which will cause any substantial flow through the longer tubes may create too great a vclocity in the shorter tubes.

The Word tubes as here used is intended to give a visualization of the phenomena which take place; and it is not to be understood that a group of distinct, continuous tubes must be used. On the contrary, an'y porous material can be utilized provided the pores or passages meet the requirements described as applying to tubes and with porous material the surface is very great, so that the eects of the electrical adsorption phenomena are strengthened. With porous niaterial, it is important that the pores onpas'- sages bemaintained of uniform size, -or a substantial difference in size of the passages will cause the large tubes to permit a greater velocity and at the same time there will be larger space to be. covered by the electric field. Further, with porous material, ar-

rangement should be made so that the force of gravity is about equal on all parts of the filter, that is, the fiowshould be approximately vertical rather than horizontal.

An apparatus illustrating the foregoing principles, which I have found particularly eicient, is shown in the accompanying drawings. In these drawings, Fig. 1 is a transverse section, Fig. 2 a longitudinal section, and Fig. 3 a plan view (with a portion of the top plate broken away) of one form of such an apparatus;` and Figs. 4 and 5 are respectively a longitudinal and transverse'section showing a similar apparatusbiilt into the crankcase of an automobile.

In Figs. 1 to 3, the numeral 10 designates an enclosure having a removable bottom portion 12 into which oil is adapted to be intro? duced under pressure through a pipe 14. The pipe 14 is provided with an adjustable'reducing valve 16 whereby the pressure of the liquid can be maintained substantially constant. This apparatus is primarily intended for treating oil, and in order to maintain heavy grades of oil in a fluid condition. the

enclosure is provided with a heating pipe 18A through which a heating' medium may be passed; f or example, if the device is used in an automobile, the Vpipe 18 may be connected with the exhaust of the engine or with the water jacket of the engine. The enclosure 10 is provided with a'screw 20 so that entrapped-air may7 be permitted to escape. Y

The filter proper is here shown as made up of a number of layers of fabric woven in a manner similar to lamp wick, indicated at 22. j Between these layers offabric are U-shapcd plates 24 which preferably 'taper oli' to a knife l edge as shown at 26, so that there will be no open passages at the edges of these plates.

The plates and fabric are prcssed'lirmly -togethcr between end platesl28 and 30, which are connected by bolts 32. 1t will be 'noted that when Lthe bolts 32 are tightenedup, the 80 top and sides of the mass will be compressed so that they are substantially air-tight, but the part of the fabric which does not contact with the plate 24 will be pressed only sutliciently'to form approximately uniform passages through it. At the bottom edge the layers of fabric are given some pressure between bars 34 which are connected together by bolts 36. The'bolts 36 are tightened up only to such point that solid material will not read- V` ily go between the different layers of wicking"l and so that the area of uniform passages will be continueddo'wn to the bottom. Betweenv the end plates 28 and 80 runa series of collection pipes 38 which are open at the bottom as indicated at 40. These pipes connect with a header pipe 42 in end plate 28. An outlet' pipe 46 is connected to the header 42 and may be supplied with a valve 48 from which runs the pipe 50.

In operation, the enclosure 10 is filled with the liquid to be cleaned, and entrapped air is allowedv to escape by loosening screw 20. Reducing valve 16 maintains the liquid in the enclosure 10 at a pressure slightly above-atmospheric. rIhe passages in the fabric 22 willV permit the liquid to-low through but will not permit the impurities to`pass, because of the electric charge, as already has been explained. As the liquid rises'in the fabric (due to capillary action) it will flow towards the pipes 38, for the pressurein these pipes slightly lower than the pressure on', the liquid. However, this flow should be maintained at verv low Velocityfor the reasons previously set lforth.

The liquid that is collected in 'pipes 38 wilh pass intothe header pipe42 and thence out through pipe 50. Y If the pipe 50 were extended down a short distance below the casing`10,it would not be necessary to maintain any' pressure on the liquid in the casing 10, for the downward How in the pipe 50 would'ex'ertysuificient suction to cause the desired movementin' Ythe tubes to take place; 125 In this structure it will benoted that dueto the compresion, the edge'sWof-v-the fabric andY the plates 24:, form as'ubstantial' casing around the top and sides'of thewickaj f Similar apparatus is Figs. 4 130` lao and 5, except that instead of the casing 10, a casing 10 is formed integral with the automobile crankcase 52. A portion of the oil from the usual oil pump enters through pipe 14 and reducing valve 16. The end plate 28 provided with the header pipe 42 is here connected with a vertical pipe 54 which discharges upwardly into the crankcase 52.

Some ofthe benefits obtainable by the use of the systemfdescribed are shown from the following examples: f

Crankcase oil which had been used in an automobile was dissolved in ether and carefully filtered by standard laboratory methods and was found to contain 4.8% of solids by wei ht. These solids represented impurities, as t e correspondingggrade of oil before use was found to contain .02% of solids on a similar test. A portion o f the used oil was filtered in a standard type of filter such as is used on automobiles, and after passing through such filter was found still to contain 347% of solids. Another portion of the same oil was filtered 'by the system of'this application and was found to containfonly .08% solids. In other. words, one filtration by'this system restored the' oil substantially to its original puritylas regards suspended mattei'. In another case transformer oil was"sub jected to a standard breakdown test. Itwas found that sparks commenced to pass through the oil at a tension of 6,000-volts and an arc was formed at 37,000 volts. After a different portion of the same oil had been passed through a filter according to thissystem, a

tension of approximately :75,000 volts wasl necessary to start any s arking and the voltage was carried aboveJ 5,000 without an arc being formed. In this test, evidence is given both of the removal of solid impurities and also of suspended liquid impurities such as water` which will be in a dierentphase from the oil, and therefore separable by the action ofthe electrostatic charges. In other words, Iuse the expression"dierent phase to cover all cases of two immiscible bodies.

It is to b understood that while I refer to the suspen ed or dispersed material as an'impurity, it may be that this will be the more valuable component of the mixture, and for the recovery of such dispersed matter my filter is particularly efficient, due to the fact that onl .small quantities will remain in the pores. av ding the difficulty of the usual filter amasar of filtering material having minute capillary.

passages, means for contacting such mass of filtering material with the liquid to be puri? fied, means for withdrawing liquid from such mass,and means for maintaining a pressure differential between the inlet and discharge points which is of the order offrom 5 to 100 l centimeters `of water whereby the liquid is forced through the filtering material but at a velocity sufficiently low to permit the elec-p'.

trical surface charges to act to substantially prevent the passage of impurities through the a mass.

2. A filtencomprising a mass of filtering material of substantial thickness in the direction of flow having passages through it larger than impurities to be removed, but substantially free of passages s o large as to permit such impurities to pass through when a liquid containing siichimpurities is caused to flow through the filtering material under a relatively low pressure such as a pressure substantially lower than 100 centimeters of water, means for contacting such mass of filtering material with the liquid to be purified., means for withdrawing liquid from such mass, and means for maintaining a pressure differential between the inlet and discharge points which is of the order of from 5 to 100 centimeters of water whereby the liquid is forced through the filtering material but at a velocity sufficiently low to permit the electrical surface charges toact tosubstantially prevent the passage of impurities throughthe mass.k

3. 'A filter comprising a mass of compacted filtering material havin of small capillary size U passages through it but sufficiently large so that impurities to be removed would e carried through by the fluid to be purified if the fluid were forced through by a relatively high pressure such as a pressure substantially higherthan 100 centimeters of water, and substantially free of passages so large as to permit such impurities to'pass through when a liquid containing such impurities is caused4 to fiow through the filtering material under a relatively low pressure such as a pressure substantially lower than 100 centimeters of water, vmeans for contacting such mass of filtering material with the liquid to be purified, means for withdrawing liquid from such mass, and means for maintaining a pressure differentialv between the inlet and discharge points which is of the order of from 5' to 100 centimeters of water whereby the liquid is forced through the filtering material but at a velocity suliiciently low to permit the electrical surface charges toact to substantially prevent the passage of impurities through the mass.

4. A filter for purifying a fluid containing impurities of different phase, which comprises a massof porous material having passages of small capillary size but sufficiently large so that such impurities would be carried' through by such fluid if the fluid were forced through by a relatively high pressure such as a pressure substantially higher than'lOO centimeters of water, means for contacting one face of such material with the fluid to be purified, means for withdrawing the purified fluid from such mass, and means for maintaining a relatively low pressure differential between the inlet and discharge points of the order of' a pressure' differential of from 5 to 100 centimeters of water, whereby the fluid is caused to flow through the passages in the mass but at a velocity sufciently low to permit the electrical surface charges to act to substanti all prevent .the passage of such impurities t irough the mass.

5. A filtering apparatus comprising a mass vof compacted filtering material substantially free of passages sufficiently large to permit minute impurities to pass therethrough when a liquid containing such impurities is moved through suchpa'ssages at a very low rate of velocity such asa velocity of ,the order of a ow caused bycapillary attraction, but containing passages sufficiently large to lpermit substantial amounts of such impurities to pass when such liquid is moved through at a high velocity, such as a velocity resulting from a pressure differential substantially in excess of 100 centimeters of water, means for .contacting one face of such mass of filtering material with aV liquid to be purified, means for withdrawing liquid Jfrom such mass without having the liquid undergo a substantial change in direction of movement while with in the mass, vand means for maintaining a pressure differential between the inlet and discharge points of the order of from 5 to 100 centimcnters of water. i

6. A structure as specified in claim 5, in"

which the filtering material is compacted at the inlet side so as largely to prevent solid material from entering the mass of filtering material.

7. In' combination, layers of wick-like fabric with the absorptive threads running sub1 stantially in one direction, meansfor holding suchlayers firmly together, a casing for one end of such layers extending over the sides thereof, means for exposing the open end of such layers to a liquid to be filtered and means for withdrawing liquid from within such casingv and means for maintaining al pressure differential between the inlet andthe discharge point within such casing. which is of the order of from 5to 10() centimeters of water. v

8. A structure as specified in claim 7 in which such casing is formed by compressing U-shaped plates between layers of the fabric with.sufiicient pressure so that the fabric directly between such plates is substantially impermeable.

RENE AUDUBERT. 

